1. Field of the Invention
The invention relates to a charge-coupled-device image sensor, more particularly to a charge-coupled-device color image sensor which has a high sensing efficiency and which permits reductions in the software processing time, in the hardware cost and in the area occupied thereby on a semiconductor substrate.
2. Description of the Related Art
Referring to FIG. 1, a first example of a conventional charge-coupled-device color image sensor (CCDIS) is shown to comprise three linear array imagers (SA, SB, SC). Each of the linear array imagers (SA, SB, SC) comprises a plurality of photodetectors and corresponds to one of the colors red, blue and green. A charge packet of electrons is collected from each of the photodetectors, which charge packet has an amount that is directly proportional to the incident radiation at the respective photodetector. The charge packets are received at a respective output port (011, 012, 021, 022, 031, 032) via one of the transfer gates (T1, T2, T3) and one of the horizontal CCDs (C11, C12, C21, C22, C31, C32).
Note that a delay in the transmission of data occurs when an image is scanned because of the relatively large space between two adjacent linear array imagers. One frame of image data can be obtained only after collating data from the three linear array imagers. Therefore, a memory unit is required so as to store temporarily the data from each of the linear array imagers and to permit access of said data so as to complete one image data frame. The above described conventional CCDIS makes inefficient use of memory space and requires a relatively long software processing time. Note also that the area occupied by the CCDIS on a semiconductor substrate is relatively large.
A second example of a conventional CCDIS is shown in FIG. 2 to include two linear array imagers (SA1, SB1) which are arranged side by side with each other. A horizontal CCD (C2) spaces a third linear array imager (SC1) from the linear array imagers (SA1, SB1). The conventional CCDIS shown in FIG. 2 can overcome most of the drawbacks of the conventional CCDIS shown in FIG. 1. The sensing efficiency of the second conventional CCDIS, however, is relatively poor.
A third example of a conventional CCDIS is shown in FIG. 3 to comprise a plurality of photodetectors (S11, S12, S21, S22) Which generate a respective charge packet of electrons that corresponds to the incident radiation thereat. Transfer gates (T11, T12) permit the transfer of charge packets from the photodetectors to vertically arranged CCDs (CV1, CV2). Data from the vertically arranged CCDs (CV1, CV2) are received by a horizontal CCD (CH) for reception at an output port (O). Note that in the above described CCDIS construction, the space between two adjacent photodetectors is approximately equal to one picture element due to the incorporation of a plurality of horizontal and vertically arranged CCDs, thereby resulting in a relatively low sensing efficiency (typically less than 50%).